Each little sailboat, measuring about 2.75 inches (7 centimeters) long, is in fact a colony of hundreds of smaller organisms, each with a specialized function such as feeding or reproduction, researchers say. [See Amazing Photos of Jellyfish Swarms]

"They sit at the surface of the ocean and have little sails," and their movement depends on which way the wind is blowing, said Richard Brodeur, a fishery biologist at NOAA Fisheries' Newport, Oregon, research station.

Most of the time off the coast of Oregon and California, the winds are blowing toward the South, into the open ocean, Peterson said. But when big storms sweep out of the southwest — like one that hit California two weeks ago — it blows these living flotillas onto the beaches, he said. There, they usually die, giving off a bad smell as they rot, he added.

Tons of the nautical creatures can be found at sea, but they don't always come ashore, Brodeur told Live Science. But recently, huge numbers of them have been washing up on land.

"This happens every few years, where they get blown onto the beaches," said Bill Peterson, an oceanographer also stationed at NOAA Fisheries' Newport lab. In 2009 or 2010, the beach had piles of the creatures 2-feet to 3-feet (60 to 90 cm) thick, and "it stunk like heaven," Peterson told Live Science.

The animals can be found all over the world, but they mostly live in tropical or subtropical waters, Peterson said. They like warm water, which has recently been pooling off the Oregon and California coasts, he said. When you get warm water combined with storms, that's when the creatures blow ashore.

Peterson said these beach invasions don't happen every year, but there's nothing unusual about the one this year.

Editor's Note: If you have an amazing marine animal photo you'd like to share for a possible story or image gallery, please contact managing editor Jeanna Bryner at LSphotos@livescience.com.